In recent years, air cycling type air-conditioners which can operate both for room cooling and room heating have been widely spreading. FIG. 1 is a block diagram showing a schematic configuration of a conventional air cycling type air-conditioner, which includes: a compressor 1; a motor 2; a heat exchanger 3; an expander 4; four-way valves 5-7 which switch air flow paths during the room cooling or heating operation; an air suction port 8; and an air outlet port 9.
In FIG. 1, the arrows with solid lines show the air flow paths at the time of room cooling. The arrows with broken lines show the air flow paths at the time of room heating. Four-way valve 5 is provided to prevent suction of the air via suction port 8 and exhaust of the air via outlet port 9 from being replaced by each other during the room cooling and room heating operations.
More specifically, at the time of room cooling, four-way valve 5 is switched to attain communication as shown in the solid lines, so that suction port 8 communicates with an inlet of compressor 1 via four-way valve 6, and outlet port 9 communicates with an outlet of expander 4 via four-way valve 7. Conversely, at the time of room heating, four-way valve 5 is switched to communicate as shown in the broken lines, so that suction port 8 communicates with an inlet of expander 4 via four-way valve 7, and outlet port 9 communicates with an outlet of compressor 1 via four-way valve 6.
Further, at the time of room cooling, four-way valve 6 is switched to attain communication as shown in the solid lines, whereby the inlet of compressor 1 communicates with suction port 8 via four-way valve 5 and the output of compressor 1 communicates with heat exchanger 3. Conversely, at the time of room heating, four-way valve 6 is switched to obtain communication as shown in the broken lines, so that heat exchanger 3 communicates with the inlet of compressor 1, and the outlet of compressor 1 communicates with outlet port 9 via four-way valve 5.
Moreover, at the time of room cooling, four-way valve 7 is switched to attain communication as shown in the solid lines, so that heat exchanger 3 communicates with the inlet of expander 4, and the outlet of expander 4 communicates with outlet port 9 via four-way valve 5. Conversely, at the time of room heating, four-way valve 7 is switched to realize communication as shown in the broken lines, and thus, suction port 8 communicates with the inlet of expander 4 via four-way valve 5, and the outlet of expander 4 communicates with heat exchanger 3.
Thus, during the room cooling operation, the air taken in from suction port 8 is directed via four-way valves 5 and 6 to compressor 1, which compresses the received air to produce high-temperature, high-pressure air. This high-temperature, high-pressure air is directed via four-way valve 6 to heat exchanger 3, in which the air is cooled by heat exchange with refrigerant air or refrigerant water. Further, the cooled, high-pressure air is directed via four-way valve 7 to expander 4, in which the air is adiabatically expanded to low-temperature, normal-pressure air. The resultant air is then exhausted via four-way valves 7 and 5, from outlet port 9.
Conversely, at the time of room heating, the air taken in from suction port 8 is directed via four-way valves 5 and 7 to expander 4, which produces low-temperature, low-pressure air. This low-temperature, low-pressure air is directed via four-way valve 7 to heat exchanger 3, in which the air is heat exchanged with refrigerant air or refrigerant water, whereby normal-temperature, low-pressure air is obtained. Further, this normal-temperature, low-pressure air is directed via four-way valve 6 to compressor 1, in which the air is adiabatically compressed, and high-temperature, normal-pressure air is obtained. The resultant air is exhausted via four-way valves 6 and 5, from outlet port 9. Compressor 1 is driven by motor 2 as well as by motive energy generated by expander 4.
As explained above, in the conventional air cycling type air-conditioner, compressor 1, motor 2, heat exchanger 3, expander 4, and three four-way valves 5-7 are used to selectively perform the room cooling or heating operation.
For the conventional air cycling type air-conditioners as described above, various techniques have been proposed to improve the efficiency of the entire devices. For example, the invention disclosed in Japanese Patent Laying-Open No. 4-184049 is directed to improve the efficiency of the air-conditioner as a whole. In this air-conditioner, compressor 1 is cooled at the time of room cooling, by condensation water generated at heat exchanger 3 or expander 4. Heat exchanger 3 is also cooled by the condensation water, which is sprayed thereon and, when evaporating, removes the heat of vaporization from heat exchanger 3.
The invention disclosed in Japanese Patent Laying-Open No. 5-223375 relates to an air cycling type air-conditioner provided with control means for reducing the rotation number of motor 2 driving compressor 1 in the case where the temperature of the air released from expander 4 attains a prescribed temperature or below, to prevent freezing of the moisture contained in the air from expander 4.
These techniques proposed, however, have not solved the following problems inherent in the conventional air cycling type air-conditioners:
(1) The humidity of the air to be exhausted to the room is uniquely determined based on the temperature and humidity of the air sucked from the room and a temperature requested of the supply air. Thus, the temperature and the humidity critical to the performance of the air-conditioner cannot be controlled simultaneously.
(2) During the room cooling operation, the moisture included in the suction air is also cooled and condensed by heat exchanger 3 or expander 4 simultaneously. Thus, if the humidity in the room is high, the efficiency of the air-conditioner as a whole decreases. This may also cause rusting inside the air-conditioner.
(3) In the case where the air of low temperature is sucked into the air-conditioner, ice particles may be blown off from outlet port 9 when the air released from expander 4 is exhausted to the room. Therefore, the temperature of the air cannot be made at or below the freezing point.
(4) Generally, the absolute humidity of the supply air is desired to be lower during the room cooling operation and to be higher during the room heating operation with respect to the absolute humidity of the suction air. In the conventional air-conditioners, however, the absolute humidity of the supply air cannot be made higher than that of the suction air during the room heating operation.
The present invention is directed to solve the above-described problems. The first object of the present invention is to provide an air cycling type air-conditioner which can control the temperature and humidity simultaneously.
The second object of the present invention is to provide an air cycling type air-conditioner which prevents a decrease in the efficiency of the air-conditioner as a whole even in a room with high humidity, and also prevents rusting inside the air-conditioner.
The third object of the present invention is to provide an air cycling type air-conditioner which prevents ice particles from blowing off even when the temperature of air is set at or below the freezing point.
The fourth object of the present invention is to provide an air cycling type air-conditioner which can set the absolute humidity of supply air higher than that of suction air at the time of room heating.